Rock treatment



3,091,935 Patented June 4, 1963 3,091,935 ROCK TREATMENT Frank Brown,Summit, and John H. Prichard, Springfield,

N ..l., assignors, by mesne assignments, to American Cyanamid Company,Wayne, N.J., a corporation of Maine No Drawing. Filed Aug. 13, 1957,Ser. No. 677,824

8 Claims. (CI. 61-36) This invention relates to a method for reinforcingstratified rock against structural failure under load and particularlyfor reinforcing the roof of a subterranean cavity which is below a layerof stratified rock. The invention also relates to the reinforcedStratified rock produced by the aforesaid method.

In the excavation of subterranean cavity, such as a mine, tunnel or bombshelter the layer of material immediately above the cavity is subjectedto severe loading due to the weight of the layers above it and due tothe lack of immediate vertical support beneath it. In order to preventthe roof of the cavity from caving in it is necessary to reinforce it orsupport it.

In the excavation of bituminous coal for example, where coal seams arefound beneath layers of shale, it has been necessary to leave pillars ofcoal as supports for the shale as entry is made into the mine. After thecoal around the pillars is mined by this method, retreat mining iscarried out, wherein the coal pillars are systematically mined and themine roof is deliberately caved in as the miners retreat.

Even with the use of pillars of coal for support, it is necessary tosupport the roof between pillars. Three methods of support are commonlyused:

1. Timber props are used, both with and without cross beams.

2. Angle iron is used (H-beams or rail-iron) in a similar manner as thetimber props or by grouting into the side walls.

3. Bolting is used wherein a hole is drilled into the ceiling 4 to 6feet deep and a /2 inch bolt of appropriate length with an expansionshield at the top is inserted. On tightening the bolt the shield expandsand grips the surrounding area.

The success of bolting is due to the fact that structural failure of ashale roof is caused by the layers of shale sliding over each other.Bolting prevents such sliding. The application of severe loading in adirection transverse to the horizontal layers of shale causes the shaleto be deformed into an inverted arch and causes the outer (or lower)layers of lengthen in comparison with the inner (or upper) layers. Whenthe layers slide over each other, all of the tension must be borne bythe outermost layer of shale which ruptures easily since it is weak intensile strength. On the other hand if the layers are prevented fromsliding over each other the tension is borne by many thicknesses ofshale and no one thickness has its tensile strength exceeded.

It is an object of this invention to provide a novel method forreinforcing the roof of a mine or other sub.- terranean cavity.

It is a further object of this invention to provide a novel method ofbonding layers of shale or other stratified rock to each other toprevent them sliding with respect to each other under load. It is afurther object of this invention to produce a reinforced stratifiedrock.

These and other objects are obtained by preparing a structurallyreinforced stratified rock having between its strata a reaction productof (a) a condensation product of an alpha, beta-ethylenicallyunsaturated dibasic acid with a dihydric alcohol and (b) anethylenically unsaturated reactant with said condensation product whichis capable of intimate admixture therewith. The reinforced stratifiedrock is prepared by applying a mixture of (a) and (b) between the strataof the rock and copolymerizing the same.

Preferably, the mixture of the condensation product and theethylenically unsaturated reactant therewith is applied between theshale layers in a mine roof by pressure injection through holes in theshale drilled for the purpose. Preferably the mixture should be ofrelatively low viscosity to permit penetration between the layers andshould be capable of curing in one hour or less at 70 F. in order toavoid delays in mining operations.

The condensation product of the alpha, beta-ethylenically unsaturateddibasic acid and the dihydric alcohol is an ethylenically unsaturatedlinear unsaturated polyester and may be made from a mixture ofunsaturated dibasic acids and/or a mixture of dihydric alcohols. Ifdesired, a portion of the unsaturated dicarboxylic acid may besubstituted by a dicarboxylic acid Without ethylenic unsaturation as acondensation product with the dihydric alcohol.

Among the acids with alpha, beta-ethylenic unsaturation which may beused are maleic acid, fumaric acid, methyl maleic acid, methyl fumaricacid, itaconic acid, dimethylmaleic acid, glutaconic acid, chlormaleicacid. Anhydrides of the acids may be used when available and it is to beunderstood that the term acid as used herein also encompasses theanhydride.

Among the acids without ethylenic unsaturation which may be used arephthalic acid, isophthalic acid, terephthalic acid, adipic acid, sebacicacid, tetrachlorophthalic acid, succinic acid, azelaic acid, glutaricacid, pimelic acid, 3,3 dipropionic acid and mixtures thereof. Theseacids are preferably used in molar proportions up to about 96%, based onthe total number of moles of diacid used.

Among the dihydric alcohols which may be used are 1,2-propylene glycol;ethylene glycol; diethylene glycol; triethylene glycol; 1,3-propy1eneglycol; dipropylene glycol (1,2); dipropylene glycol (1,3); 2,3-butyleneglycol, and neopentyl glycol. Halogenated glycols such as 2,2bis-chloromethyl 1,3-propanediol and 2,2 bis-bromomethyl 1,3-propanediolmay also be used.

It is to be noted that dihydric alcohols containing ether linkages, suchas diethylene glycol, may be used. It is also within the scope of thisinvention to use as a dihydric alcohol, a derivative of more highlyhydroxylated compound, such as a monoether or a monoester of glycerm.

The molar proportions of total dicarboxylic acid to total dihydricalcohol may vary between about 1.0 to about 0.8.

In a preferred modification, an unsaturated polyester resin is preparedby reacting 50 mole percent of phthalic anhydride and 50 mole percent ofmaleic anhydride with a 10 percent molar excess of 1,2-propylene glycoluntil the resin has an acid number of about 50. The excem propyleneglycol is distilled olf leaving a solid, hard, brittle unsaturatedpolyester resin which may be readily crushed and which is stable instorage.

Styrene is preferred as the ethylenically unsaturated reactant with theunsaturated polyester. Styrene is a solvent for the polyester and isthus capable of intimate admixture therewith. Among the otherethylenically unsaturated reactants with the unsaturated polyester whichmay be used are methyl methacrylate, vinyl acetate, ethyl aerylate anddiallyl phthalate. These compounds 00- polymerize with the unsaturatedpolyester in situ to produce stable space polymers of high molecularweight. The styrene or equivalent is generally blended with theunsaturated polyester in amounts between 15% and 50% by weight, based onthe weight of the polyester.

The blend of the unsaturated polyester and the styrene,

for example, copolymerizes when subjected to heat or to the action of anappropriate polymerization catalyst. When used to reinforce a mine roof.the application of heat is not practical and the action of a catalyst,particularly a catalyst which is effective at temperatures not higherthan 90 F., is preferred. Among the catalysts suitable for such use arethe organic peroxides and hydro peroxides such as benzoyl peroxide,lauroyl peroxide. In some cases, a polymerization accelerator, such asdimethylaniline or cobalt naphthenate may be required to activate thecatalyst at the desired temperature. The peroxides are generallyincorporated into the blend in amounts between about /z% and 2% byweight based on the total weight of the blend.

The Styrene or other reactant with the ethylenically unsaturated linearpolyester copolymerizes therewith by linking a carbon atom at anethylenic bond on one linear polyester molecule with a carbon atom at anethylenic bond on another. in order to obtain a reaction, intimateadmixture between the two components must be achieved. Generally, thepolyester is soluble in the ethylenically unsaturated comonorner, suchas styrene. In some cases, both components are soluble in a commonsolvent.

In a preferred embodiment, the aforementioned unsaturated polyesterresin is dissolved in styrene. the styrene comprising 30% by weight ofthe entire blend.

Fifty parts by weight of the aforementioned blend is added to fiftyparts by weight of a styrene solution of a polyester of ethylene glycolwith 60 mole percent of adipic acid, 30 mole percent of phthalic acidand mole percent of maleic anhydride. The styrene solvent in the latterblend also comprises by weight of the entire blend.

The combined blend is then divided into two equal portions with twoparts of benzoyl peroxide added to one portion and two parts ofdimethylaniline added to the other. The portions are reblended andapplied between the rock strata to cure Within a few hours at 90 F. toform an excellent bond between the strata.

In a qualitative bond strength test a bonded area be tween two slatetiles 2.8 inches square withstood more than 150 lbs. of weight in directtension without rupturing the bond.

In another preferred embodiment, the aforementioned condensation productof l.2--propylene glycol with equimolar portions of phthalic anhydrideand maleic anhydride is dissolved in styrene, as above, sulli-cient toproduce a solution containing 30% of styrene. A small amount (0.05% byweight) of cobalt naphthenate is ineluded as an accelerator.

Seventy-five parts by weight of this colbalt naphthenatecontainingsolution is blended with twenty-five parts by weight of the abovedescribed styrene solution of ethylene glycol condensation product withadipic acid. phthalic acid and maleic anhydride. The total blend isdivided into two portions as above with two parts by weight of benzoylperoxide added to one and two parts by weight of dimethylaniline addedto the other. The portions are reblended and applied between rock stratafor about a half hour at 90 F. to form an excellent bond between thestrata.

In a bond strength test a bonded area between two slate tiles 2.8 inchessquare withstood more than 400 lbs. of direct tensions before the slatebroke in shear without rupturing the bond.

In a flexural test of the identical polyester blend, but cured at 77 F.and applied between slate tiles one inch square, the bond withstood aflexural load of 500 pounds although the slate broke at that load. Thistest unequivocably shows the bond to be strong in both tension andshear.

in applying the last described polyester blend to the rock strata of ahorizontal bed of shale, which is overhead in a mine roof, a series ofholes /2 inch in diameter and 5 feet deep are drilled 6 feet apart in afreshly excavated area of square feet. The polyester blend, preferablyhaving the catalyst added at the site is injected into the holes at apressure of 600 pounds per square inch. The polyester is permitted tocure for about 1 hour at the mine temperature of 55 F. The roof is thensafe enough to permit the excavation to advance.

It is to be understood that the foregoing detailed description is merelygiven by way of illustration and that many variations may be madetherein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by LettersPatent is:

1. A method of reinforcing the roof of a subterranean cavity which isbelow a layer of Stratified rock which comprises drilling a series ofspaced holes upwardly into said Stratified rock in a directiontransverse to the direc tion of the strata of said rock and injectingthrough said holes, under pressure, between the strata of the rock amixture of an ethylcnically unsaturated linear polyester and anethylenically unsaturated reactant with said linear polyester which iscapable of intimate admixture therewith and allowing said mixture tocure.

2.. The method of claim 1 wherein said polyester mixture is capable ofcuring at 70 F. within one hour.

3. A method of reinforcing the roof of a subterranean cavity which isbelow a layer of shale which comprises drilling a series of spaced holesupwardly into said shale in a direction transverse to the direction ofthe strata of said shale and injecting through said holes. underpressure, between the strata of the shale a mixture of a condensationproduct of an ethylenically unsaturated dibasic acid with a dihydriealcohol and an ethylenically unsaturated reactant with said condensationproduct which is capable of intimate admixture therewith and allowingsaid mixture to cure.

4. A method of reinforcing the roof of a subterranean cavity which isbelow a layer of Stratified rock which comprises drilling a series ofspaced holes upwardly into said stratified rock in a directiontransverse to the direction of the strata of said rock and injectingthrough said holes, under pressure, between the strata of the rock amixture of a condensation product of an cthylenically unsaturated linearpolyester and an ethylenically unsaturaated reactant with said polyesterwhich is capable of intimate admixture therewith, and an organicperoxide curing catalyst and allowing said mixture to cure.

5. A method of reinforcing the roof of a subterranean cavity which isbelow a layer of shale which comprises drilling a series of spaced holesupwardly into said shale in a direction transverse to the direction ofthe strata of said shale and injecting into said holes, under pressure,a mixture of a condensation product of an ethylenically unsaturated dibaic ac d with a dihydric alcohol. styrene and an organic peroxide curingcatalyst and allowing raid mixture to cure.

6. A method of reinforcing the roof of a subterranean cavity which isbelow a layer of shale which comprises drilling a series of spaced holesupwardly into said shale in a direction transverse to the direction ofthe strata cf said shale and injecting into said holes, under pressure,a mixture of a condensation product of malcic anhydride and1,2-propylene glycol, styrene and bcnzoyl peroxide as a curing catalystand allowing said mixture to cure.

7. The method of claim 6 wherein said holes are approximately /2" indiameter and six feet apart and wherein said mixture is injected intosaid holes at a pressur: of about 600 pounds psi.

8. A method of stabilizing underground rock formations which form mineroofs which comprises: drilling a hole into a rock formation havingzones of weakness and which is subject to failure in tension as well asshear, injecting under pressure into said hole and through said holeinto the rock formation a formation adhesive rezin which is liquid andself-curing at ambient temperatures,

and which is selected from the group consisting of solutions of linearpolyesters in liquid monomeric unsaturated polymerizable compoundscontaining an alphabets ethylenie iinkage, said solutions alsocontaining a peroxide type catalyst and a cobalt promoter, whereby saidresin flows into and filis said zones of weakness and cures in position,thereby adhesively uniting said formation at the zones of weakness, andstabilizing said rock formation against roof falls.

References Cited in the file of this patent UNITED STATES PATENTS

8. A METHOD OF STABILIZING UNDERGROUND ROCK FORMATIONS WHICH FORM MINEROOFS WHICH COMPRISES: DRILLING A HOLE INTO A ROCK FORMATION HAVINGZONES OF WEAKNESS AND WHICH IS SUBJECT TO FAILURE IN TENSION AS WELL ASSHEAR, INJECTING UNDER PRESSURE INTO SAID HOLE AND THROUGH SAID HOLEINTO THE ROCK FORMATION A FORMATION ADHESIVE RESIN WHICH IS LIQUID ANDSELF-CURING AT AMBIENT TEMPERATURES, AND WHICH IS SELECTED FROM THEGROUP CONSISTING OF SOLUTIONS OF LINEAR POLYESTERS IN LIQUID MONOMERICUNSATURATED POLYMERIZABLE COMPOUNDS CONTAINING AN ALPHA-BETA ETHYLENICLINKAGE, SAID SOLUTIONS ALSO CONTAINING A PEROXIDE TYPE CATALYST AND ACOBALT PROMOTER, WHEREBY SAID RESIN FLOWS INTO AND FILLS SAID ZONES OFWEAKNESS AND CURES IN POSITION, THEREBY ADHESIVELY UNITING SAIDFORMATION AT THE ZONES OF WEAKNESS, AND STABILIZING SAID ROCK FORMATIONAGAINST ROOF FALLS.